TIJUANA, Mexico (Reuters) - Seventeen teenagers, many accused of working as hitmen for drug gangs, escaped from a juvenile detention center near the U.S. border on Thursday after digging through an outer wall, police said.

The boys, suspected young drug cartel members often dubbed "narco juniors," scraped a large hole through a brick wall using an iron rod at bedtime in the center in Tijuana, across the border from San Diego, California, a police spokesman said.

"They made a hole and no one noticed. Then they hit two guards with the rod and made it through the wall," said the spokesman for Baja California state police, who asked not to be quoted by name.

Police launched a search backed by helicopters. Mexico has experienced more than 20 jailbreaks this year. President Felipe Calderon has made crushing the drug violence the centerpiece of his presidency.

In May, drug hitmen dressed as police screeched up to a northern Mexico prison in a convoy of vans and freed 53 prisoners who were seen on security cameras pouring into the street.

In Tijuana, most of the escaped teenagers were accused of trafficking drugs or working as hitmen in the rowdy border city.

But due to their status as minors, they cannot be imprisoned or charged with federal drug crimes under Mexican law and were being held in the detention center.

Some 12,800 people have been killed in Mexico's three-way drug war between rivals and the country's security forces since late 2008 in a conflict that worries investors and Washington and is increasingly drawing in young people.